Strongly Coupled Bacteriochlorophyll Dyad Studied Using Two-dimensional Phase-modulated Fluorescence-detected Electronic Spectroscopy

TL;DR

This paper demonstrates the first use of phase-modulated fluorescence-detected 2D electronic spectroscopy to analyze coherences and kinetics in a strongly coupled bacteriochlorophyll dyad, revealing vibrational and relaxation dynamics.

Contribution

It introduces a novel application of phase-modulated F-2DES for analyzing coherences and kinetics in photosynthetic model systems.

Findings

Vibrational frequency observed matches that in monomers.

Picosecond relaxation timescale between excited states.

First demonstration of coherence and kinetic analysis with F-2DES.

Abstract

Fluorescence-detected two-dimensional electronic spectroscopy (F-2DES) projects the third-order non-linear polarization in a system as an excited electronic state population which is incoherently detected as fluorescence. Multiple variants of F-2DES have been developed. However, none have demonstrated analysis of kinetics and coherences routine in photon-echo 2DES. Here, we report phase-modulated F-2DES measurements on a strongly coupled symmetric bacteriochlorin dyad, a relevant 'toy' model for photosynthetic energy and charge transfer. Coherence map analysis shows that the strongest frequency observed in the dyad is well-separated from the excited state electronic energy gap, and is consistent with a vibrational frequency readily observed in bacteriochlorin monomers. Kinetic rate maps show a picosecond relaxation timescale between the excited states of the dyad. To our knowledge this is the first demonstration of coherence and kinetic analysis using any variant of F-2DES.